Internal combustion engines generally comprise at least one piston movable within a cylinder by a crank shaft. When an intake passage is opened, the piston moves downwardly to draw a fuel-air mixture into the cylinder for combustion. As the piston reaches the bottom of the cylinder, the intake passage will close and the piston will rise compressing the fuel/air mixture. After combustion, the exhaust gases escape from the cylinder through an exhaust passage.
Typically, engines are generally designed with the opening of the intake valve and the closing of the exhaust valve occurring at a fixed time. The timing and duration of the valves in these engines are usually designed based upon the particular application of the engine and may not be changed to increase engine horsepower.
Rotary valves may be used to manage the flow of the gases into and out of the cylinder of the engine. Rotary valves have been developed to adjust the timing and duration of the valves of an engine. For example, U.S. Pat. No. 3,993,036 shows a rotary valve having a spring loaded sleeve at the trailing edge of the rotary valve. Although the sleeve may retard the closing of the valve, the sleeve does not allow for adjustment of the opening of the valve. Further, the sleeve may only retard the closing of the valve at high revolutions per minute (r.p.m.) of the engine. The complexity of the valve may also increase the manufacturing and repair costs, and the timing and duration of the valve may not be controlled upon command during engine operation.
U.S. Pat. No. 4,163,438 shows rotary valves that may be axially displaced in a cylinder head to change the timing of the valves. However, the air flow through the valves may be restricted when the timing of the valves is changed. Further, as the r.p.m. of the engine increases, it may be desirable to provide greater air flow into the combustion chamber. It may also be difficult to keep the valves cool because the axial movement of the valves. As a result, the valves may overheat. Additionally, the complexity of the valve assembly may increase manufacturing and repair costs.
U.S. Pat. No. 4,421,077 shows flappers positioned near the leading and trailing edges of an intake rotary valve. The flappers may increase the length of the port of the intake rotary valve, allowing the timing of the valve to change. However, the opening of the flappers depends upon the pressure across the opening of the intake valve, and the flappers will usually only open at high r.p.m. Further, the timing of valves may not be controlled upon command during engine operation.
U.S. Pat. No. 5,205,251 discloses a rotary valve disposed within a rotatable sleeve. The sleeve has openings on opposing sides in order to change the timing of the valve. However, when changing the timing of the valves, the closing of the intake valve and the opening of the exhaust valve will usually be changed. Further, the air flow through the valve may be restricted when the timing of the valves is changed. The complexity of the valve assembly may also increase manufacturing costs and the costs of repair.
U.S. Pat. No. 5,392,743 discloses a single rotary valve positioned on a shaft that is axially displaced by a cam to varying an open duration of the valve. However, when changing the duration of the valve, the exhaust may contaminate the intake charge by diluting the intake mixture and thereby reducing engine efficiency. Further, the complexity of the valve assembly may increase manufacturing and repair costs.
Accordingly, there exists a need for an engine with improved valve timing control that can adjust the opening of the intake valve and closing of the exhaust valve. It is desirable to change the timing of the valves without restricting the air flow through the valves at higher r.p.m. It would also be beneficial to change the timing of the valves upon command.